Saturday, 19 May 2012

A geostationary satellite is a satellite that is stationary with respect to the earth and appears to be fixed in sky. In a satellite TV, receiving antenna remains pointed towards the satellite at the same position in the sky. The receiver need not move to track the satellite. This is an example of geostationary satellites.

Geostationary satellites are positioned at a height of about 35,786kms above the ground and rotate in the direction of the earth’s rotation. They rotate around the earth at the same speed as that of earth’s rotation as this height. As a result, they remain stationary above a point on the earth. Since geostationary satellites are stationary, they are ideal for use as communications satellites. They may also used for weather observations, and remote imaging as they can repeatedly scan the same points on the earth beneath them.

A geostationary satellite can provide coverage over about 40% of the planet because of its great height. However, they cannot provide coverage at the Northernmost and southernmost latitudes. This is because these satellites circle the earth at the equator.

A satellite in an orbit near the earth must travel faster than one in a geostationary orbit because the pull of gravity is stronger closer to the earth. That is why satellites in low altitude orbits constantly change their position in relation to the surface of the earth. The major difference between such satellites and geostationary satellites is that they can scan different areas of the earth at relatively infrequent periods.